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One of the country’s most popular lifestyle drugs turns 15 on Wednesday.

And if that doesn’t put a smile on the face of any of the thousands of celebrities, and the growing number of millennials who use it, well, it could mean they’re using too much of it.

We’re talking Botox, the drug from Allergan that has rung up sales of roughly $21.1 billion since it came on the market in 2002 — smoothing out countless wrinkles, crow’s feet and other age-related skin divots Botox, along with Prozac and Viagra, is among three lifestyle drugs — a prescription troika most associated with improving the quality of life rather than curing its diseases — and is, quite literally, changing the face of celebrity America.

“People used to think they had to live with what they wore born with,” says Marian Salzman, a futurist and social media expert who serves as CEO of Havas PR. “Then orthodontics came along and introduced a new mindset.”

Kelly Ripa, Simon Cowell, Jenny McCarthy and Courtney Cox are just four of the many celebrities who have copped to using Botox.

While Botox rung up $2.8 billion in global revenue last year — more than the $1.2 billion in sales for Viagra — Pfizer’s 19-year-old erectile dysfunction drug outsold the wrinkle-eraser over its first 15 years $27.1 billion to $21.1 billion, according to industry estimates.

Eli Lilly lost its US patent protection for Prozac in 2001.

The 7.1 million Botulinum Toxin Type A procedures recorded for 2016 accounted for 46 percent of all minimally invasive cosmetic procedures in the country, according to statistics published by the American Society of Plastic Surgeons.

And the growth in Botox procedures since 2000 came in at a chart-topping 797 percent.

“It can’t make a woman turning 40 look 21, but it can freeze her face to look 39 for a good 20 years,” Salzman says. “It’s here to stay — at least for those who can afford it.”

Dr. Matthew Schulman, a board-certified plastic surgeon on Manhattan’s Upper East Side, puts the cost of Botox injections at $300 per area.

The three most common areas — often serviced in a single visit — are around the eyes (crow’s feet), the forehead (creases) and between the eyebrows (“11” frown lines).

This has a standard treatment costing $900 for injections with “a duration of action of three months,” Schulman says.

Botox’s growing reputation as a low-risk proposition has served it well.

Schulman says he had “a spike in male patients when the economy got really competitive a decade ago,” creating an influx of procedures that hasn’t lessened.

New clients, he adds, are as likely to be in their 20s instead of the 40-plus set initially drawn to Botox. “They’re millennials, and they’re influenced more by social media than by celebrities,” Schulman says.

Futurist Salzman also credits social media for the “mainstreaming” not only of Botox but of plastic surgery in general.

“People are sharing their tummy tucks on Pinterest, which even I consider too much information,” she says.